Process fluid or gas bearings are now being utilized in an increasing number of diverse applications. These fluid bearings generally comprise two relatively movable elements with a predetermined spacing therebetween filled with a fluid such as air, which, under dynamic conditions forms a supporting wedge sufficient to prevent contact between the two relatively movable elements.
More recently, improved fluid bearings, particularly gas bearings of the hydrodynamic type, have been developed by providing foils in the space between the relatively movable bearing elements. Such foils, which are generally thin sheets of a compliant material, may be deflected by the hydrodynamic film forces between adjacent bearing surfaces and the foils thus enhance the hydrodynamic characteristics of the fluid bearings and also provide improved operation under extreme load conditions when normal bearing failure might otherwise occur. Additionally, these foils provide the added advantage of accommodating eccentricity of the relatively movable elements and further provide a cushioning and dampening effect.
The ready availability of relatively clean process fluid or ambient atmosphere as the bearing fluid makes these hydrodynamic, fluid film lubricated, bearings particularly attractive for high speed rotating machinery. While in many cases the hydrodynamic or self-acting fluid bearings provide sufficient load bearing capacity solely from the pressure generated in the fluid film by the relative motion of the two converging surfaces, it is sometimes necessary to externally pressurize the fluid between the bearing surfaces to increase the load carrying capacity. While these externally pressurized or hydrostatic fluid bearings do increase the load carrying capacity they do introduce the requirement for an external source of clean fluid under pressure.
Illustrative of hydrodynamic and/or hydrostatic bearing patents assigned to the same Assignee of this application are U.S. Pat. Nos.: 3,215,479, 3,215,480, 3,366,427, 3,375,046, 3,382,014, 3,434,761, 3,434,762, 3,467,451, 3,511,544, 3,560,064, 3,615,121, 3,635,534, 3,642,331, 3,677,612 and 3,893,733.
It is common practice when mounting the individual foils to one of the relatively movable elements to affix one end of the foil to the element in some fashion. The most common practice, as exemplified in U.S. Pat. Nos. 3,366,427, 3,375,046 and 3,615,121, is to attach a rod or bar to the end of the foil which can then be retained in a slot or groove in one of the relatively movable elements. Alternately, as exemplified in U.S. Pat. No. 3,382,014, a plurality of overlapping foils may be individually mounted on a foil base such as by spot welds. The base would then be frictionally held against one of the relatively movable elements. Further a lip or projection at one end of the foil may be restrained in a slot or groove in one of the relatively movable elements. Examples of this type of mounting can be found in U.S. Pat. Nos. 3,511,544, 3,747,997 and 3,809,443.
While anchoring the bearing foil or foils at one end continues to be satisfactory for many foil bearing applications, this type of mounting does present certain inherent limitations and disadvantages. For example, mounting the foil at one end, particularly a longer foil, introduces a tendency for the foil to tighten up during start-up while the two relatively movable members are rubbing. To overcome this wrap or tightening, higher torque is required before lift off (i.e., establishment of the fluid film between adjacent surfaces) occurs. This tendency is much more marked in conical bearings since the foils are forced into a converging sway space under axial load, the so-called "Chinese finger effect." Also there are situations in which the foil lips or anchors can be pulled out of their slots or grooves so as to bind movement between the two relatively movable members. When thin foils are used to improve the surface compliance, flutter and instability can be introduced. On the other hand, when higher stiffness is employed in lieu of damping to reduce resilient frequency amplitudes, higher starting torques are required for end mounted foils. There is no convenient place to apply effective damping except the beam load supports at the ends of these foils where they are mounted.